Redistribution of ERK/MAP kinase to uropod-like structures in interleukin-3-induced cell shape changes

[Novel Tyrosine Phosphorylation Signals in the Nucleus and on Mitotic Spindle Fibers and Lysosomes Revealed by Strong Inhibition of Tyrosine Dephosphorylation]

Protein-tyrosine phosphorylation is one of the posttranslational modifications and plays critical roles in regulating a wide variety of cellular processes, such as cell proliferation, differentiation, adhesion, migration, survival, and apoptosis. Protein-tyrosine phosphorylation is reversibly regulated by protein-tyrosine kinases and protein-tyrosine phosphatases. Strong inhibition of protein-tyrosine phosphatase activities is required to undoubtedly detect tyrosine phosphorylation. Our extremely careful usage of Na₃VO₄, a potent protein-tyrosine phosphatase inhibitor, has revealed not only the different intracellular trafficking pathways of Src-family tyrosine kinase members but also novel tyrosine phosphorylation signals in the nucleus and on mitotic spindle fibers and lysosomes. Furthermore, despite that the first identified oncogene product v-Src is generally believed to induce transformation through continuous stimulation of proliferation signaling by its strong tyrosine kinase activity, v-Src-driven transformation was found to be caused not by continuous proliferation signaling but by v-Src tyrosine kinase activity-dependent stochastic genome alterations. Here, I summarize our findings regarding novel tyrosine phosphorylation signaling in a spatiotemporal sense and highlight the significance of the roles of tyrosine phosphorylation in transcriptional regulation inside the nucleus and chromosome dynamics.

Chemokine-mediated inflammation: Identification of a possible regulatory role for CCR2

The chemokine receptor CCR2 binds four pro-inflammatory monocyte chemoattractant proteins, designated MCP1/CCL2, MCP2/CCL8, MCP3/CCL7 and MCP4/CCL13. This study demonstrates the important biology of this receptor during the response to the chemokine milieu. Competitive chemotaxis and calcium flux assays were performed utilising mixtures of chemokines to assess a hierarchal arrangement of chemokine prepotency; these demonstrated that the MCP2-CCR2 interaction is able to supersede signals generated by RANTES, another pro-inflammatory chemokine, or the homeostatic chemokine SDF1. These observations were validated using three physiologically relevant monocytic cell lines. Having identified the importance of CCR2, experiments were then performed to examine the signal transduction processes coupled to this receptor. G protein coupling was initially examined; Cholera toxin reduced the chemotactic response to MCP2 (p<0.001), whilst the response to the other MCP chemokines remained normal. The response to MCP2 was uniquely inhibited by elevated concentrations of cAMP and, unlike MCP1, 3 and 4 (p<0.05), MCP2 failed to inhibit adenylate cyclase. Expression of dominant negative H-ras demonstrated that each MCP chemokine required active ras in order to elicit ERK activation and a chemotactic response. Unlike MCP1, MCP2 failed to induce nuclear translocation of activated ERK1 or subsequent induction of c-Myc expression. Akt activation also showed ligand-specific differences, with MCP2 producing a delayed response compared to the other MCP chemokines. Together these data highlight the importance of CCR2 and suggest that it is a powerful tool for fine tuning the immune response.

Trafficking of Lyn through the Golgi caveolin involves the charged residues on alphaE and alphaI helices in the kinase domain

Src-family kinases, known to participate in signaling pathways of a variety of surface receptors, are localized to the cytoplasmic side of the plasma membrane through lipid modification. We show here that Lyn, a member of the Src-family kinases, is biosynthetically transported to the plasma membrane via the Golgi pool of caveolin along the secretory pathway. The trafficking of Lyn from the Golgi apparatus to the plasma membrane is inhibited by deletion of the kinase domain or Csk-induced “closed conformation” but not by kinase inactivation. Four residues (Asp346 and Glu353 on αE helix, and Asp498 and Asp499 on αI helix) present in the C-lobe of the kinase domain, which can be exposed to the molecular surface through an “open conformation,” are identified as being involved in export of Lyn from the Golgi apparatus toward the plasma membrane but not targeting to the Golgi apparatus. Thus, the kinase domain of Lyn plays a role in Lyn trafficking besides catalysis of substrate phosphorylation.

Oncogenic and invasive potentials of human macrophage-stimulating protein receptor, the RON receptor tyrosine kinase

The product of the RON (recepteur d'origine nantais) gene belongs to the MET proto-oncogene family, a distinct subfamily of receptor tyrosine kinases. The ligand of RON was identified as macrophage-stimulating protein (MSP), a member of the plasminogen-related growth factor family. RON is mainly expressed in cells of epithelial origin and is required for embryonic development. In vitro RON activation results in epithelial cell dissociation, migration and matrix invasion, suggesting that RON might be involved in the pathogenesis of certain epithelial cancers in vivo. Indeed, recent studies have shown that RON expression is significantly altered in several primary human cancers, including those of the breast and colon. Truncation of the RON protein has also been found in primary tumors from the gastrointestinal tract. These alterations lead to constitutive activation of RON that causes cell transformation in vitro, induces neoplasm formation in athymic nude mice, and promotes tumor metastasis into the lung. Studies employing transgenic models further demonstrated that over-expression of RON in lung epithelial cells results in multiple tumor formation with features of large cell undifferentiated carcinoma. The oncogenic activities of RON are mediated by RON-transduced signals that promote unbalanced cell growth and transformation leading to tumor development. Thus, abnormal accumulation and activation of RON could play a critical role in vivo in the progression of certain malignant human epithelial cancers.